Mn-rich graftonite, ferrisicklerite, stanekite and Mn-rich vivianite in a granitic pegmatite at Soe' Valley, central Alps, Italy.

Mn-rich graftonite, (Ca,Mn2+)(Fe2+,Mn2+)2(PO4)2, ferrisicklerite, Li1x(Fe3+,Mn2+)PO4, manganoan apatite, (Ca,Mn2+,Fe2+Mg)(PO4)3Cl, stane? kite, Fe3+Mn2+O(PO4) and Mn-rich vivianite, (Fe2+)3(PO4)28H2O, occurring in a granitic pegmatite at Soe` Valley (central Alps, Italy) were characterized by powder and single-crystal X-ray diffraction (XRD) and electron microprobe analyses. Geochemically, the Mn-rich graftonite phases are poorly evolved Fe/Mn-phosphates of rare-earth elements-lithium (REE-Li) granitic pegmatites. The assemblage Mn-rich graftonite + ferrisicklerite + stane?kite has rarely beendocumen ted in pegmatites. Inthe Soe` Valley pegmatite, ferrisicklerite forms exsolution lamellae with Mn-rich graftonite associated with manganoan apatite and stane?kite. Graftonite is associated with Mn-rich vivianite. Powder and single-crystal XRD data indicate that the unit-cell volume of graftonite increases as a function of Mn2+ content. Stane?kite shows a distinctly smaller unit-cell volume with respect to previously reported stane?kites, probably due to reduced Mn2+. Vivianite with significant Mn2+ has a unit-cell volume similar to nearly Mn-free vivianite. The formation of Mn-rich graftonite and manganoan apatite is related to destabilization of Mn-rich almandine and biotite during pegmatite formation. Ferrisicklerite forms exsolution lamellae along the 010 cleavage planes of Mn-rich graftonite, whereas stane?kite forms by alterationof ferrisicklerite and Mn-rich vivianite due to circulation of late-stage hydrothermal fluids.